"How could we easily tell if trading had been haulted?"

A halt trading order is issued by the approriate exchange, and it then goes out to multiple wire services.  If you want to, youj can use something like "Yahoo! Finance" to select trading symbols on which you want special notices of news releases, including halt trading orders.

Or, watch here as many of us receive such notices, and will report anything relevant as soon as we see it.

VP